The technical field of this disclosure is brake fluid reservoirs. In particular, a brake fluid reservoir is provided with a single sensor for detecting a condition of low fluid level in the reservoir as well as brake lining wear.
Hydraulic braking systems have typically been the basis for vehicle braking systems, especially automotive braking systems. Hydraulic systems are used to convert fluid pressure into linear and/or mechanical motion. Such systems allow the source of the hydraulic pressure to be positioned remotely from the cylinders that affect the braking action. These systems comprise an actuator, such as a brake pedal, reservoir fluid which is responsive to pressure applied by the actuator, (such as a master cylinder) and means for converting the hydraulic pressure to a braking force, generally fluid cylinders. Mechanical braking pressure is achieved by utilizing the force of the depression of the brake pedal by the driver to increase the pressure on the master cylinder. Such systems are typically accompanied by a vacuum boost that multiplies the force supplied to the brake pedal, throughout the braking operation. The increased pressure in the master cylinder is then transmitted through fluid lines to the fluid cylinders. The fluid cylinders operate the calipers thereby forcing the calipers and brake pads against the rotors and/or drums which slows the vehicle by frictional force.
Hydraulic systems of the above-described type have many disadvantages. These include the large amount of volume and mass that the master cylinder, vacuum booster, ABS modulator and hydraulic lines add to the completed vehicle. Installation of standard hydraulic braking systems is also complicated and labor intensive. Additionally, the large number of parts and installation also adds to repair and maintenance issues as individual parts reach the end of their useful life. A variant form of applying a vehicle brake system is referred to as a brake by wire brake system (BBW). BBW describes the ability to activate vehicle wheel brakes via an electric signal generated by an onboard processor/controller as a result of input signals thereto. Brake torque is applied to the wheels without direct mechanical interaction between the vehicle""s brake pedal and the wheel brake.
A particular type of BBW systems is known as a xe2x80x9cdry interface cornerxe2x80x9d system (DIC). The typical DIC system operates when a driver inputs a force to the brake pedal. A force sensor and travel sensor attached to the pedal transmits an electronic signal to an electronic controller, which in turn sends the signal to the self contained braking device typically located at each wheel of the vehicle. The DIC system is known as a hybrid system in that electric signals are used to generate the type and amount of braking force required at each wheel of the vehicle with electrical wires rather than standard hydraulic brake lines. Located at each corner of the vehicle is a self-contained module which takes the electrical signal and mechanically brakes the vehicle. The self-contained module utilizes an individual motor that drives a ball screw piston assembly that pressurizes hydraulic brake fluid to ultimately apply the brake caliper to a rotor at that corner of the vehicle. Such a DIC system significantly reduces assembly cost. The individual modules can be separately assembled and fluid filled prior to the manufacture of the vehicle. DIC modules then only need to be bolted to the automobile during the assembly process and plugged in using standard electrical connections. Thus, reliability and quality control of the overall brake system is also increased. Finally, the elimination of hydraulic lines stretching throughout the vehicle as well as the elimination of the master cylinder, booster, and ABS modulator reduces space requirements within the engine compartment.
Brake cylinder fluid level can presently be determined from visual inspection of the reservoir. Some master cylinder reservoirs include reed sensors to detect low fluid level. Typical master cylinder assemblies use a single reservoir to feed multiple wheel brake assemblies. Reed sensors positioned in the reservoir are commonly used to indicate low fluid level by sending a signal to trigger an indicator, such as a warning light, in the vehicle. Because the reservoir on these systems feeds two or more wheel brake assemblies, a specific location and cause of the low fluid level is not identified.
Brake lining wear in some systems can be detected by manual inspection. In recent years lining wear sensors of variant and different forms have been placed on the brake pad. One form of brake pad sensor gives off a noise that is audible to the driver as an indication that the brake linings are worn down to a predetermined point. Another form of sensor has an electrical connection to provide a warning light within the vehicle when the brake lining is worn down to a predetermined point. Although these systems can be reliable, it is not cost effective to place sensors directly on the brake pads.
It would be desirable to have a sensor system that would overcome the above disadvantages.
An aspect of the present invention provides a sensor system for detecting lining wear and fluid level in a dry interface corner actuator reservoir assembly when each actuator is used with a single wheel brake. Included as part of the actuator reservoir is a reservoir assembly. The reservoir assembly includes a reservoir for containing fluid for the actuator and a sensor assembly positioned in the reservoir as part of a cap assembly having a single set point to indicate both low reservoir fluid level and a need for brake lining replacement.
Other aspects of the invention provide a reservoir that can be sized to hold a predetermined volume of fluid. The single set point can be based on the predetermined volume of the reservoir. The sensor assembly can further include a cylinder, a float including a sensor activator positioned within the cylinder, and a sensor switch positioned adjacent the cylinder wherein the reservoir is sized to hold a predetermined volume of fluid and the sensor switch has a single set point to allow the sensor switch to indicate both low fluid level and brake lining replacement when activated by the sensor activator.
The sensor activator can include a magnetic ring attached to the float that activates the sensor switch when the fluid in the reservoir is at a predetermined level. The sensor can be electrically connected to a warning device through an opening in a valve stem of the reservoir cap assembly.
Another aspect of the present invention includes a method for single sensor indication of an abnormal leak condition or normal low reservoir fluid and brake lining wear condition in a single wheel brake dry interface corner actuator including positioning a sensor having a single set point in a reservoir portion of a reservoir assembly, tripping the single set point when fluid in the reservoir reaches a predetermined level and sending an indication of one of a leak condition and/or a brake lining wear condition from the sensor.
Another aspect of the present invention includes a sensor system for detecting lining wear and fluid level in a dry interface corner actuator for a single wheel brake including means for positioning a sensor having a single set point in a reservoir portion of a reservoir assembly, means for tripping the single set point when fluid in the reservoir reaches a predetermined level, and means for sending an indication of one of a leak condition and/or brake lining wear condition.